Linear condensation polymers



Patented Feb. 1 6, 1937 UNITED. STATES PATENT OFFICE LINEAR CONDENSATIONPOLYMERS No Drawing. Application January 2, 1935, Serial N0. 180

20 Claims.

This invention relates to compositions of matter, and more particularlyto new polyamides.

This case is a continuation in part of my application Serial No. 548,701filed July 3, 1931.

In the mentioned application I have described fiber-forming polymersamong which are synthetic linear condensation polyamides formed byreacting organic diamines with dibasic acids or with the amide-formingderivam tives of dibasic acids, and polyamides formed from polymerizableamino acids. The claims in this application are directed generally topolyamides capable of being formed into useful fibers and specificallyto such polyamides comprising polymerized amino acids, the fiber-formingpolyamides derived from diamines and dibasic acids being specificallyclaimed in my application Serial Number 74,811, filed April 16, 1936.

With regard to the amino acid polymers, it is well known that certainamino acids and derivatives of amino acids can be caused to react withthemselves with the formation of polyamides. Thus, according to Curtiusand Benrath (Ber. 37, 1279 (1904)) the simplest of the amino acids,glycine, loses water at high temperature furnishing a product consistinglargely of tetraglycyl glycine:

sumcmcoon mugcmco i (NHCH COhNHCILCOOH 41120 It is known further thatG-aminocaproic acid polymerizes at high temperature yielding chiefly alinear polyamide whose structure can in part be represented by thegeneral formula (See Gabriel and Maas, Ber. 32, 1266 (1899); v. Braun,Ber. 40, 1840 (1907) Carothers and Berchet, J. Am. Chem. Soc. 52, 5289(1930). The ethyl ester of fi-aminocaproic acidalso polymerizes atelevated temperature with the loss of ethyl alcohol yielding a polymerof the same general type. In a similar manner 7-aminoheptoic acidNH2(CHz) aCOOH is largely converted to a 45 polyamide when it is causedto react with itself by heating to an elevated temperature. (Manasse,Ber. 35, 1367 (1902); v. Braun, Ber. 40, 1840 (1907)). However,polyamides having unit lengths greater than 8 do not appear to have beendescribed and no polyamides have been described that have the remarkableproperties of those of the present invention.

This invention has as an object the preparation of new and usefulproducts of high molec- 55 ular weight. A further object is to preparenew polyamides from amino acids. A further object is to prepare fromamino acids polyamides which can be drawn into fibers. A still furtherobject is to prepare strong, pliable, highly oriented fibers.

These objects are accomplished by the following invention whichcomprises polymerizing an amino acid or a derivative of the amino acidand continuing the polymerization by heat treatment until the productformed is capable of being drawn into a continuous filament.

The polyamides with which the present invention is concerned are derivedfrom amino acids. These polyamides may be represented in part by thegeneral formula .N(R)R-C ON(R)RCON(R)RC 0-. in which the number of atomsin the chain of the recurring unit N(R)R'CO derived from the amino acidis referred to herein as the unit length.

Amino acids of the formula generally present the formal possibility ofpolymerizing or condensing with themselves by the elimination of water,e. g., 2NH(R)R000H NH R RC0N(R)R'c00H+H,0

NH(R)RCO0H+NH(R)RCON(R)RCOOH NH(R)R'GON(R)R'CON(R)RCO-OH+H,0,etc. In theabove formulae R. is a divalent organic radical and R is a univalentorganic radical or hydrogen. The condensation products just illustratedmay be referred to as linear polyamides. Their molecules are chainsbuilt up from the radicals or units N(R)RCO which may be called thestructural units of the polymers. These units are formally derived fromthe amino acids by the elimination of Water. The number of atoms in thechain of this unit may be called the unit length. The following exampleswill illustrate the meaning of this term:

Unit length Formula of Structural acid unit mqww

. into a polyamide having an average molecular amides of highermolecular weight which are then capable of being drawn into continuousfilaments.

My process comprises as a first step the conversion in any convenientmanner of the amino acid or a suitable derivative of the amino acidweight not less than twice that of the amino acid, and as a second stepthe conversion of the non-fiber-forming polyamide into the fiberforminghigh molecular weight polyamide. Thus, in the above mentioned first stepthe acid may be heated at atmospheric pressure and at a temperature of75 to 275 C. but preferably above C. until more than 0.5 mole of wateris formed for each mole of acid used, or an alkyl or aryl ester of theacid may be heated similarly until at least 0.5 mole of alcohol orphenol is formed for each molecule of alcohol used. A typical productobtained in accordance with the first step has a molecular weight in theneighborhood of 800-1200.

The temperature used in the final polymerization of the second stepshould be above"150 C. and preferably in the range of to 275 C. Thereaction is preferably carried out under pressures which permit theready distillation of the liberated water, alcohol, or phenol. Reducedpressures are preferred although atmospheric pressure may be used. Thetemperature indicated will vary somewhat with the nature of the aminoacid from which the polyamide is derived. In the absence of a solvent ormedium, the final stage of the reaction must be carried out at atemperature above the melting point of the polyamide. The time andpressure required in the final stage to produce a polymer suitable forspinning will depend in part on the size of the batch and in part on theamount of surface it presents. The final stage of the reaction may behastened by stirring the reaction mixture or by bubbling through it orpassing over it an inert gas such as nitrogen. A factor that must bekept in mind, however, is that the final reaction mass conducts heatvery slowly and if local cooling takes place in the interior of themass, solid particles or lumps will tend to separate causing incompletereaction. For this reason, if a gas is passed through the reactionmixture it should preferably be preheated.

In accordance with the preferred practice of the present invention thepolymerization of amino acids having a unit length of at least 7 iscarried out in the manner described above which results in a highmolecular product having properties quite different from the polyamidesheretofore prepared. In order that the polyamide have a unit lengthgreater than 6 the amino acid (which for the present purpose means alsothe appropriate derivative) from which the polyamide is madeshould beone in which there are at least 5 atoms in the chain separating thecarboxyl group and the amino or substituted amino group. An example ofan amino acid having the minimum limitation just mentioned isG-aminocaproic acid,

NH2 (CH2) 5COOH,

which yields by the methods described hereinafter a polyamide,[NH.(CHz)5.COlx, having a unit length of 7. The subscript a: in this andin similar formulae given in this specification represents a largeindefinite integral number. My new superpolymers made in accordance withthe preferredmethod just mentioned yield on acid hydrolysis amino acidsin which the amino and carboxyl groups are separated by a chain of atleast 5 atoms.

The essential feature of the present invention is the furtherpolymerization, under suitable conditions, of low molecular weightfusible or soluble polyamides which have more than two structural unitsand are derived from monoaminomonocarboxylic acids, the polymerizationbeing continued untila product capable of being drawn into continuousfilaments is formed.

While my invention is most easily operated with low molecular weightpolyamides derived from amino acids having unit lengths of at leastseven, it is also applicable to certain polypeptides or to the aminoacids from which they are derived (unit length=3). However, I have notsucceeded in preparing useful products from amino acids having unitlengths of 5 and 6 because these acids do not appear to be polymerizableunder ordinary conditions.

As mentioned above, the polyamide resulting from the reaction in thefirst stage is converted into a superpolymer by further heatingpreferably in the molten condition and preferably under a good vacuum(below 20 mm.). The heating is continued until the polymerizationreaction has proceeded far enough to give a readily spinnable product.The time of heating required varies with different amino acids and aminoacid esters. If the heating period is continued too far beyond theoptimum, which must be determined by experiment for each compound,

inferior products are obtained. A molecular 1 still may be used in thepreparation of the superpolyamides but generally conventionaldistillation apparatus is satisfactory. The superpolyamides can often beprepared by heating the polyamide at atmospheric pressure.

As described in the above mentioned application, the polyamides derivedfrom diamines and These polymers also dissolve more slowly than the lowpolymers and solution is preceded by I swelling. As already mentioned,the high polymers can be spun into continuous highly oriented filamentswhereas the low polymers cannot. In

general the low polymers can be converted into high polymers by acontinuation of the reaction by which the low polymers were formed or,for example, by further heating at higher temperature under conditionsthat permit the rapid re moval of any readily volatile products. Thenecessary conditions vary according to the particular case as isindicated in the discussion of various factors presented above, butinpractice the conversion to high polymer is easily tested for merely bytouching the surface of the molten polymer with a rod and drawing therod away. If high polymer is present a continuous filament ofconsiderable strength and pliability is readily formed. This simple testis easily used to 'control the completion of the reaction. The length ofthe heat treatment necessary to obtain products of optimum utility forspinning must be determined for each polymer. If the heat treatment iscontinued after this optimum has been reached, inferior products areobtained.

The high molecular weight polyamides of this invention are all capableof being spun into continuous filaments. The spinning may be carriedout, in a number of ways. That is, the polyamide may"'be dissolved in aitable solvent and the solution extruded through orifices into acoagulating bath, the resulting filament being continuously collected ona suitably revolving drum or spindle. Or, the extruded solution may bepassed through a heated chamber where the solvent is removed byevaporation. The properties of the polyamides of this invention alsomake it possible to spin the molten material directly without theaddition of any solvent or plasticizer. For this purpose a mass of themolten polymer may be touched with a rod. Upon drawing the rod away afilament is formed. The filament may be caught on a moving drum or reeland in this manner a continuous filament may be drawn from the moltenmass until the latter is exhausted. The cross-section of the filamentsthus obtained can be regulated by controlling the temperature of themolten mass and the rate of reeling. The higher the temperature and themore rapid the rate of reeling, the finer will be the filament.

Continuous filaments may also be produced by extruding the moltenpolyamide through an orifice and continuously collecting theextrudedfilament on a rotating drum. The fineness of the filaments maybe controlled by controlling the temperature of the molten polymer, theamount of pressure applied, the size of the orifice, and the rate ofreeling. The properties of the polyamides of this invention make itpossible to obtain exceedingly fine filaments, as fine as 0.2 denier orless.

A remarkable characteristic of filaments of the polyamides of thisinvention is their ability to accept a very high degree of permanentorientation under stress. Filaments obtained by spinning the polyamidesunder such conditions that very little stress is applied very closelyresemble the polymer from which they are drawn. In particular, whenexamined by X-rays they furnish X-ray powder difiraction patterns, butby the application of moderate stress at ordinary temperature thesefilaments can be instantly elongated or cold-drawn as much as ZOO-700%.This cold drawing is accompanied by a progressive increase in tensilestrength until a definite limit is reached beyond which the applicationof additional stress causes the fiber to break. The cold drawn fibersremain permanently extended, they are much stronger than the materialfrom which they are drawn, more pliable and elastic, and when examinedby X-rays they furnish a sharp fiber difiraction pattern. They alsoexhibit strong birefringence and parallel extinction when observed undercrossed Nicols' prisms.

This evidence of fiber orientation shows that the cold drawn filamentsare true fibers.

In practice, the formation of continuous oriented fibers from thefilaments of this invention is easily conducted as an integral part ofthe spinning operation. Thus the extruded filaments as they arecollected may be transferred continuously to a second drum driven at ahigher rate of speed, so as to provide any desired degree of stretchingor cold drawing. 0r friction devices may be inserted between the twodrums to provide the necessary stretch. It may be observed that thisprocess of cold drawing difiers from the stretch-spinning known to theartificial fiber art in that it may be carried out very rapidly andcompletely-in the total absence oi any solvent or plasticizer.

The following examples are further illustrative of the methods used incarrying out my invention:

Example I Polyamide, CH2 aCONH]x; unitlength, 10. In making thepolyamide, five and one-half grams of ethyl-Q-aminononanoate,

NHz (CH2) sCOOCzHs was heated under atmospheric pressure at 205- 2l0 C.during four hours. The alcohol which distilled of! (B. P. 75-80 C.)weighed 1.0 g. as compared with a theoretical value of 1.1 g. forcomplete reaction. The product which remained as a residue in thereaction vessel was a polyaminononanoylnonanoic ester. When cold it wasa hard, rather tough, opaque horny solid which melted to a very viscousliquid at about 195 C. The material did not string out into filamentswhen it was touched with a rod and the rod withdrawn. This viscouspolymer was then heated at 220-240 C. under 1 mm. pressure during eighthours. The heating was accompanied by a progressive increase inviscosity.

The superpolymer (4 g.) obtained in accordance with the foregoingexample was grey, hard, and horn-like. It melted to a transparent massthat was barely capable of flowing at 195-198 C. without decompositionand had a density of 1.067. It was insoluble in common solvents underordinary conditions. Boiling formamide partially dissolved the polymer,and it was completely soluble in boiling phenol. Liquid ammonia at -80C. had no effect. The polymer could be readily drawn into strong,pliable filaments as is illustrated below.

Short filaments are produced by touching the molten polymer with astirring rod, and drawing the rod away. Continuous uniform filamentshaving a diameter of 0.007 mm. or less were easily prepared as follows:The molten polymer was extruded from a spinneret having an orifice madefrom a number 20 hypodermic needle (diameter of bore 0.47 mm.) andmaintained at 208-210 C. by means of an enveloping copper blockelectrically heated. The gauge pressure required to extrude the polymerfrom a number 1 20 needle at 210 C. was 8-10 pounds. A smaller needlerequired a greater pressure for the extrusion; for example, 30-35 poundspressure was used with a. number 23 (diameter of bore 0.31 mm). Theextruded filament was reeled up on a motor driven drum at the rate of 70ft./min.'

and simultaneously wound up (cold drawn) on a second drum at the rate of270 tt./min. corresponding to 286 per cent elongation. Spinning at evenhigher degrees of stretch are possible, the maximum lying in theneighborhood of 500%. The cold drawn filaments are strong, tough,pliable, lustrous, and permanently oriented.

Measured strengths of filaments spun from the polyamide ((CHz)aCONH7Xvary over a considerable range, since they depend upon the fineness ofthe filament, the degree of stretch used in spinning, and various otherfactors. In general, however, the strengths are considerably higher thanthose observed for other forms of artificial silk. Typical values are 2to 5 g./d. or

20 to 50 lag/mm. with the denier varying from i 3 g. to 1.2 g. forfilaments stored at 25 C, 50% relative humidity. It may be added thatthe strength of the polyamide fibres is unusually insensitive toconditions of temperature or humidity. These values compare veryfavorably with those for cotton (28 kgJmm. or 2 g'./d.) and silklrg./mm. or 4 g./d.).

The polyamide fibers also show exceptionally good elastic behavior. Inthis respect they are much superior toexisting artificial sillrs. Theelastic behavior depends to a certain extent on the amount of stretch orcold drawing used in the spinning operation; the more complete the colddrawing, the more perfect is the elastic behavior. Typical data onelastic recovery of fibers from the polyamide [(CHzMCONT-lh are shownbelow.

Percent of cold Duration drawing in Stretch of 9 spinning stretch News yPercent Percent Seconds Percent 286 8.0 180 78 302 9. 8 l00 88 502 9. 7100 03 This recovery is almost instantaneous.

( (CH2) aCONH-) 2:

showed that the spun polyamide readily and permanently absorbed from aweekly acid medium those dyes ordinarily used for silk and wool.

X-ray photographs of the polyamide made as described in the foregoingexample were made of the polymer in its massive state (solid polymerbefore spinning) and in the forgn of cold drawn filaments. The massivepolymer gave a powder X-ray difiraction pattern, indicating that it hasa crystalline structure. The filaments gave a sharp fiber diffractionpattern which clearly shows that the cold drawn filaments are truefibers and show orientation along the fiber axis. The fiber structure isdeveloped during the process of cold drawing. The fibers also exhibitstrong birefringence and parallel extinction when observed under crossedNicols prisms.

The fibers made in accordance with the present invention are practicallyinsensitive to moisture as shown by the following experiment in which0.3468 g. of the above mentioned dry fibers (dried by heating. for 18hours at 100 C.) was placed in a room maintained at 25 C. and relativehumidity. After five hours exposure the fibers weighed 0.3484 g.,indicating a 0.46% increase in weight due to moisture absorption.Viscose rayon under these conditions absorbs about 8% water.

The remarkable wet strength of my new fibersactress of 3.8 g. per denierand a wet strength of 4.2 g. per denier. Most artificial fibers have amuch lower wet strength than dry strength; for example, a sample ofviscose rayon was found to have a dry strength of 1.05 g.-per denier anda west strength of 0.57 g. per denier while a sample of celluloseacetate rayon gave values of 1.59 g. per denier and 0.76 g. per denierfor the dry and wet strengths, respectively.

Example H Polyamide, [(CH2)10CONH]2:; unit length, 12.

By heating l1 aininoundecanoic a c i d, NHziCHz) mCOOI-l', for one-halfhour at 220-225 C. it readily polymerized with the liberation of water.The product which remained as a residue in the reaction vessel was awhite, opaque, hard, rather tough mass which melted to a very viscousliquid at about 180 C. It was polyaminounclecanoyl aminoundecanoic acid.When this molten polymer was touched with a rod and the rod withdrawn itddnot yield any filaments. In order to obtain aspinnable polymer, thisproduct was heated for 3.5 hours at 220-225 C. at a pressure less than 1mm. of mercury. The resulting polymer melted at 180 C. and was easilyspinnable.

Following the general procedure described in Example I filaments werespun from this polyamide. In a typical experiment the conditions were asfollows: diameter of orifice, 0.47 mm; temperature, 196 0.; pressure, 4pounds; spinning rate, '70 ft./min.; cold drawing rate, 300 ft./min.;elongation, 330 per cent; denier of filament, 7.6 g. The filamentsobtained in this way had a silky appearance. Other properties of thefilaments observed were M. P. I'M-178 C.; denier at break, 5.0;elongation, 552 per cent; tenacity, 2.7 grams per denier.

Example III uid at about 147 C. It was almost completely devoid ofspinning properties. The yield was quantitative. This product wastransformed into polyamide having excellent spinning properties by 20hours additional heating at 225-230 C. under 2. pressure of less than 1mm. The resultant product melted at 147-150" C.

Example IV Polyamide [(CHzhCONHh; unit length, 7.

Approximately 50 g. of fi-aminocaproic acid was heated for 0.5,.' nourat 220-225 0-. at atmospheric pres'sure -"wNe'arly the theoreticalamount of water distilled off during this period. The residue was a hardopaque solid. Itwa's a polyamide of G-aminocaproic acid mixed with asmall proportion of the corresponding monomeric lactam,

rwnmco It did not show any spinning properties. This material was heatedfurther at 225230 C. under a pressure less than 1 mm. of mercury. Asmall amount of the monomeric lactan was removed in this way and theresidue was converted into a spinnable superpolymer. The 'superpolyamidewas a hard, tough, opaque, white mass which melted at 205-210 C. to atransparent mass that was barely capable of flowing. The polymer hadexcellent spinning properties, yielding strong, pliable, highly orientedfibers. It dissolved readily in hot glacial acetic acid, and the polymerwas precipitated as a fiuify fllar mass when the solution was pouredinto water. The polymer also dissolved in cold concentrated sulfuricacid yielding a clear very viscous solution without any evidence ofrapid degradation and the polymer was recovered as a fiuffy filar masson pouring the solution into water.

Example V Polyamide, [(CH2)5CONH]X unit length, '7.

Ethyl S-aminocaproate (7.2 g.) was heated at -180 C. for 4 hours.Approximately 1.5 g. of ethanol distilled off during this operation. Thepolymer formed in this manner was not spinnable. It was heated for 18hours at 220-240 C.-under less than 1 mm. pressure. Two grams of thelactam were collected as a distillate during the heating under reducedpressure. The superpolymer finally obtained melted at 200-203 C. and wasreadily spinnable.

Example VI Polyamide, [(CHzhCONHh; unit length, 9.

A sample of B-aminocaprylic acid was heated at 220-240 C. for 10 hoursat atmospheric pressure under conditions that permit the readydistillation of water. The residual polyamide obtained in this manner isa tough, opaque solid which when molten is readily spun into strong,pliable, highly oriented fibers.

The preparation of polyamides is not limited to the use of the aminoacids and derivatives cited in the foregoing examples. Amino acidscontaining a primary amino group, NHz, react most readily but aminoacids containing a secondary nitrogen group, e. g., NHCHa, are alsooperative. The preferred polyamides can be represented by the generalformula in which R represents hydrogen or a univalent organic radical,such as allgvl; in which R represents a divalent hydrocarbon orsubstituted hydrocarbon radical containing at least 5 atoms in thechain; and in which :2: represents the number of structural units in thepolyamide molecule.

Among other amino acids which may be used in the preparation of thepolyamides are the following:

tional advantages.

chain of at least 5 atoms. Polyamides of fiberforming qualities can beobtained by substituting an amino acid, such as NH2(CH2)3COOH, for partof the higher amino acid (higher in the sense that the amino andcarboxyl groups are further removed in the chain).

In the preparation of the polyamide the amino acid or ester maybe heatedto reaction temperature, usually 75-200 C., in a closed vessel or in anopen reactor. When an open reactor is used, the rate and extent of thereaction can be determined by measuring the water or alcohol removed. Ifan ester is to be used in the preparation of the polyamide, it isgenerally desirable to select an ester of a low boiling alcohol, e. g.,methyl, ethyl, and isobutyl alcohols. The phenyl esters may also beused. The reaction may be carried out in the presence of a diluent orsolvent. It is also within the scope of this invention to carry out thereaction in the presence of an inert gas, such as nitrogen. Super orsub-atmospheric pressure may be used. Following the initial heatingperiod (either in the open or closed vessel), the polyamide is heatedabove its melting point, generally ZOO-275 C. and preferably under agood vacuum (less than 5 mm.) in order to promote further polymerizationto a product (superpolymer) of good spinning properties.

A catalyst, e. g., a metal or metal salt, may be used in the preparationof the polyamide but is not necessary. For example, a polyamide similarto that described in Example I can be obtained by. heating the ethylester of Q-aminononanoic acid with a small amount of sodium. In aspecific experiment the polyamide melted at -200 C. In general, no addedcatalysts are required in the above described processes of the presentinvention. It should be mentioned, however, that the surface of thereaction vessel (e. g., glass) appears to exercise a certain degree ofcatalytic function in many cases. The use of added catalysts may alsoconfer addi- Examples of such materials are inorganic materials ofalkaline reaction such as oxides and carbonates, and acidic materialssuch as halogen salts of polyvalent metals.

The polyamides of this invention compared with most organic compoundsare unusually resistant to oxidation. Nevertheless, at the hightemperatures used in their preparation they show a strong tendency tobecome discolored in the presence of air. For this reason, it isdesirable to exclude air or to limit the access of air during theirpreparation. This may be done by the usual methods, e. g., by operatingin a closed vessel during the early stages of the reaction, or, if anopen vessel is used, by providing a stream of inert gas. One of theprincipal and NHaCHlCHOC 0 0H.

Derivatives of the acid, such as the ester or acid halide, may be used.It is also possible to use mixtures of the amino acids in thepreparation of the polymers. In the preparation of mixed polyamides itis not necessary for the best results that all the amino acidsrepresented have the amino and carboxyl groups separated by a CHPCHIGHCOOHI CHs-C I advantages of operating under'diminished pressure in thelater stages of the reaction also is the fact that this greatly cutsdown on the incidence of air. It is helpful in some cases to addantioxidants to the reaction mixture, especially antioxidants such assyringic acid that show very little inherent tendency to discolor.

molecular weight products as are the superpolymers in general disclosedin my mentioned copending application, the minimum molecular weightsprobably being not substantially less than 10,000. The solubilitycharacteristics of the polyamides, however, make accurate molecularweight determinations difllcult.

The polyamides of this invention are for the most part relatively highmelting solids insoluble in most common organic solvents butgenerallysoluble in hot formamide, phenol, or in acids, such as hydrochloric,sulfuric, or acetic,

Generally the melting point decreases and the soluoility increases withincrease in the unit length of the recurring unit in the polyamide. Theyare very resistant to hydrolysis especially toward alkaline hydrolyticreagents, and they show little or no tendency toward decomposition untiltemperatures above 220 C. are reached. On pro- 'longed heating withdilute mineral acids, however, they are hydrolyzed, yielding themonomeric amino acids from which they were derived. The polyamidesgenerally yield sharp X-ray powder diffraction patterns.

The superpolyamides of this invention are especially valuable, becausethey can be drawn or spun into strong, tough, pliable fibers. By theaction of stress these fibers can be permanently stretched, elongated,or cold drawn as much as sixor seven-fold. The cold drawn fibers show agreatly increased strength and pliability, and they are highly orientedalong the fiber axis as is shown by the fact that they are birefringent,and they furnish a sharp and well developed fiber diffraction patternwhen examined by X- rays. The oriented fibers of this invention are inmany cases much stronger than any known artificial fibers and are muchmore resistant toward the action of water, chemical agents, and hightemperature.

It will be apparent from the foregoing that the invention describedherein affords a method for the preparation of high melting, relativelyinsoluble products by a simple process. The high softening temperatureand the insolubility of the products render them particularly suitablefor the preparation of fibers. Fibers prepared from these products areinsensitive to moisture and solvents and can be pressed with a hot iron.This synthesis of fiber-forming products is unique in that the productsare synthesized from low molecular weight, monomeric, non-fibrousmaterials. This is quite different from the preparation of fibrousmaterials, such as cellulose acetate, ethyl cellulose, etc., in whichhigh molecular weight (polymeric) fibrous materials synthesized bynature are used as starting materials. Polyamides may also be used asingredients in molding, coating, and impregnating compositions.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claims.

I claim:

l. A process which comprises heating an amide forming compound of theclass consisting of polymerizable monoaminomonocarboxylic acids havingat least 5 carbon atoms in the chain separating the amino and carboxylgroups and amide forming derivatives thereof until a product is formedwhich is capable 6f being drawn into The fiber-forming orsuperpolyamides are high continuous filaments, the nitrogen atom of saidamide forming compound carrying at least one hydrogen atom.

2. A step in a process for making polymeric materials which comprisessubjecting an amino oacid polyamide derived from a polymerizablemonoaminomonocarboxylic acid having at least 5 carbon atoms in the chainseparating the amino and carboxyl groups and incapable of being drawninto continuous filaments to continued polymerizing heat treatment untilthe product formed is capable of being drawn into continuous filaments.

3. A process which comprises polymerizing by heat treatment a substanceof the class consisting of amino acids and amide forming derivativesthereof, said substance having at least five carbon atoms in thechainseparating the carboxyl group and the amino group, said amino grouphaving at least one hydrogen atom on the nitrogen, and continuing thepolymerization treatment until the product formed is capable of beingdrawn into continuous filaments 4. A process which comprisespolymerizing by heat treatment a substance of the class consisting ofamino acids and amide forming derivatives thereof, said substance havingat least five carbon atoms in the chain separating the carboxyl groupand the amino group, said amino group having at least one hydrogen atomon the nitrogen, and

continuing the polymerization treatment until the product formed iscapable. of being drawn into continuous filaments which show bycharacteristic X-ray pattern orientation along the fiber axis.

5. A process which comprises polymerizing by heat treatment a substanceof the class consisting of amino acids and amide forming derivativesthereof, said substance having at least five carbon atoms in the chainseparating the carboxyl group and the amino group, said amino grouphaving at least one hydrogen atom on the nitrogen, and continuing thepolymerization treatment in vacuum until the product formed is capableof being drawn into continuous filaments.

6. A polyamide having recurring structural units of the general formulain which R represents hydrogen or a. univalent hydrocarbon radical and Rrepresents a divalent hydrocarbon radical having a chain of at leastfive carbon atoms, said polyamide being capable of being drawn intocontinuous filaments.

'7. A polyamide having recurring structural units of the general formulain which R, represents hydrogen or a univalent hydrocarbon radical and Rrepresents a divalent hydrocarbon radical having a chain of at leastfive carbon atoms, said polyamide being capable of being drawn intocontinuous filaments which show by characteristic X-ray patternsorientation along the fiber axis.

8. A polyamide having recurring structural units of the general formula.

hydrocarbon radical having a chain of at least five carbon atoms, saidpolyamide being capable of being drawn into continuous birefringentfilaments 9. A synthetic polymeric product which yields on acidhydrolysis an amino acid in which the amino and carboxyl groups areseparated by a chain containing at least 7 carbon atoms.

10. The process set forth in claim 2 in which said continued heattreatment is at a temperature not less than 150 C.

11. A process whichcomprises heating a substance of the class consistingof polymerizable monoaminomonocarboxylic acids having at least 5 carbonatoms in the chain separating the aminc and carboxyl groups and amideforming derivatives thereof at a temperature of 75 C. to 275 C. andcontinuing heating the resulting polymer at a temperature above 150 C.until the product formed is capable of being drawn into continuousfilaments.

12. A step in a process for making polymeric materials which comprisessubjecting an amino acid polyamide derived from a polymerizablemonoaminomonocarboxylic acid having at least 5 carbon atoms in the chainseparating the amino and carboxyl groups and incapable of being drawninto continuous filaments to continued polymerizing heat treatment at apressure less than 20 mm. until the product formed is capable of beingdrawn into continuous filaments.

13. A step in a process for making polymeric materials which comprisessubjecting an amino acid polyamide derived from a polymerizablemonoaminomonocarboxylic acid having at least 5 carbon atoms in the chainseparating the amino and carboxyl groups and incapable of being drawninto continuous filaments to continued polymerizing heat treatment inthe presence of an amide forming catalyst until the product formed iscapable of being drawn into continuous filaments.

14. A step in a process for making polymeric materials which comprisessubjecting an amino acid polyamide derived from a polymerizablemonoaminomonocarboxylic acidfigaving at least 5 carbon atoms in thechain separating the amino and carboxyl groups and incapable of beingdrawn into continuous filaments to continued polymerizing heat treatmentin a stream of inert gas until the product formed is capable of beingdrawn into continuous filaments.

15. A polyamide having recurring structural units of the general formulain which R represents a divalent hydrocarbon radical having a chain ofat least five carbon atoms, said polyamide being capable of being drawninto continuous filaments which show by characteristic X-ray patternorientation along the fiber axis.

16. A synthetic linear condensation polyamide capable of being formedinto fibres showing by characteristic X-ray patterns orientation alongthe fibre axis.

17. A synthetic polymer capable of being drawn into fibers showing bycharacteristic X- ray patterns orientation along the fiber axis, saidpolymer yielding, upon hydrolysis with strong mineral acid, an aminoacid containing at least five carbon atoms in the chain separating thecarboxyl group and the amino group. I

18. A synthetic linear condensation polyamide capable of being formedinto fibres showing by characteristic X-ray patterns orientation alongthe fibre axis, said polyamide being polymerized G-aminocaproic acid.

19. A synthetic linear condensation polyamide capable of being formedinto fibres showing by characteristic X-ray patterns orientation alongthe fibre axis, said polyamide being polymerized 9-aminononanoic acid.

20. A synthetic linear condensation polyamide capable of being formedinto fibres showing by characteristic X-ray patterns orientation alongthe fibre axis, said polyamide being polymerized ll-aminoundecanoicacid.

WALLACE H. CAROTHERS.

